Steerable load-carrying assemblies

ABSTRACT

A moveable load-carrying assembly including a chassis ( 1 ) having a plurality of wheels ( 6 ) arranged as a first wheel set and a second wheel set, each wheel ( 6 ) being rotatable and swivellable relative to the chassis ( 1 ); the wheels ( 6 ) of the first wheel set being connected by a first linkage ( 21 ), and the wheels ( 6 ) of the second wheel set being connected by a second linkage ( 22 ); and wherein one of the wheels ( 6 ) of the second wheel set is linked to the opposite one of the wheels ( 6 ) of the first wheel set by a link ( 11 ) such that when one of the wheels ( 6 ) of the first wheel set is swivelled in one direction relative to the chassis ( 1 ), all the wheels ( 6 ) of the first wheel set swivel in that direction in unison, and all the wheels ( 6 ) of the second wheel set swivel in the opposite direction in unison. Means are included to provide three distinct modes of operation for a wheel set, the modes corresponding to straight-line travel, fully-steerable travel and a braking mode. The assembly also includes an apparatus for returning the steerable wheels to a straight-line position, comprising a first member ( 203 ) associated with a tie rod ( 202 ) operably connected to one or more steerable wheels, at least one further member ( 205, 206 ) pivotably associated with a fixed chassis member ( 201 ) and a resilient means ( 209 ) associate with the further member.

This is a divisional of copending application Ser. No. 09/529,497 filedMay 31, 2000.

FIELD OF THE INVENTION

The present invention relates to improvements in moveable load-carryingassemblies and refers particularly, but not exclusively to a steerable,movable, load-carrying assembly. The present invention also includes acentralising mechanism for use with such load-carrying assemblies toassist in steering of the overall assembly.

DEFINITIONS

Throughout this specification reference will be made to a perambulator,pusher or push-chair for babies, invalids and the like. It should beunderstood that such preferred embodiments are given by way of exampleonly and the invention is not to be considered to be limited to suchusage. Indeed, the present invention will be suitable for use in anyassembly intended to be propelled by human effort rather than motivepower including, for example, trolleys, carts, shopping trolleys, wheelbarrows, strollers, toy prams, trailers, caravans, boat trailers,wheeled jacks for vehicles, wheel chairs, gurnies, hospital beds,hospital stretchers mounted on a wheeled base, work platforms, librarytrolleys, and other similar articles having a number of wheels and/orcastors.

Throughout this specification, reference to a wheel or wheels is to betaken as including a reference to a castor or castors, or a wheel actingas a castor.

Furthermore, throughout this specification reference to a chassis is tobe taken as including reference to a framework.

BACKGROUND OF THE INVENTION

In accordance with the known prior art, perambulators normally havefixed wheels. This gives rise to undue and undesirable hardship in theiruse. For example, the turning circle of fixed wheel perambulators can berather large, with obvious limitations and consequences. Also, there canbe scrubbing of the wheels when turning thus increasing wear.

In accordance with the prior art, moveable assemblies of theaforementioned type can be said to be one of three forms:

(i) a first where all four wheels are fixed and not in any way steerable(for example, traditional forms of perambulators);

(ii) a second (for example, child strollers and the like) having therear wheels fixed, whilst the front wheels are swivellable; or

(iii) a third where all four wheels are separately swivellable (forexample, supermarket trolleys).

In practice it has been found that each of the three forms exhibit anumber of advantages which make them suited to certain uses, but sufferfrom disadvantages which limit their suitability for all uses.

When all four wheels are fixed (the first form), one advantage is thatthe wheels can be quite large in diameter, thus allowing the assembly tomore easily traverse uneven terrain. Another advantage is that suchassemblies are suitable for use along pathways where the operator doesnot need to concentrate on manoeuvring the assembly in normal travel andonly has to do so when a change of direction is required. Therefore,when larger diameter wheels are used with fixed wheel assemblies, theride is smoother for the occupant, an important result when the occupantmay be a baby. It has also been found that fixed wheel assemblies maytraverse a slope or undulating ground without there being excessiveexertion by the operator to keep the assembly in the desired directionother than when a change in direction is required.

Such fixed wheel assemblies suffer from the disadvantage that it isdifficult to change direction. Two commonly used methods are to eitherpush down on the handle to lift the front wheels off the ground and topivot the handle horizontally to point the assembly in the desired newdirection of travel; or to lift the handle so that the rear wheels leavethe ground and to pivot the handle horizontally to achieve the desirednew direction of travel. Both of these alternatives can require theapplication of significant effort and skill.

Further disadvantages of such fixed wheel assemblies include theexcessive wear and tear on the frame component of the overall structure,which can result in the frame being bent or distorted. Furthermore, theeffort required by the operator may be excessive. As a result,assemblies of the fixed wheel type have been found to be unsuited foruse as articles such as shopping trolleys, where frequent changes indirection are required and normally within a small area.

For the second form of assembly is that with fixed rear wheels andswivellable front wheels. Such assemblies have the advantages of beingmore easily manoeuvrable, in terms of both space and effort. However,this form has the disadvantage that it is necessary to utilisesmall-diameter wheels to enable the caster-style swivel action to allowthe front wheels to rotate through 360 degrees as they are generallymounted or have to swivel under the assembly. The use of such smallerdiameter wheels make it more difficult for the assembly to traverserough or uneven surfaces, and also gives a far less comfortable ride tothe occupant when compared with larger-diameter fixed wheeledassemblies. Furthermore, the swivellable front wheels are normallycasters, or operate as caster wheels. In consequence they are not linkedtogether and individually follow the terrain which can result in theswivellable front wheels facing in different directions, making itextremely difficult for the operator to maintain control, especiallywhen the assembly is traversing a sloping surface. With such assemblies,when traversing a cambered or sloping surface it is necessary for theoperator to maintain concentration and expend a significant effort tokeep the assembly heading in the desired direction.

Assemblies with four separately swivellable wheels—the third form—havethe advantages of being: very manoeuvrable; able to turn within theirown length; and able to be used equally well and efficiently when pushedand/or pulled in either direction. Such assemblies have therefore beingfound to be specially suited for use as shopping trolleys, babystrollers and the like.

Such assemblies also exhibit a number of disadvantages. Firstly, suchassemblies are best suited for use on horizontal, flat surfaces, with itbeing difficult to maintain control when moving such an assembly acrossa slope. Furthermore, as all wheels have to be able to rotate through360 degrees, assemblies of this form can only be produced with smallerdiameter wheels, once again giving rise to a less comfortable ride forthe occupant even if the wheels are locked in the forward position,thereby allowing forward movement only. As all four swivel wheels arecaster wheel sets, all may operate independently, especially when unevensurfaces are being traversed. As the wheels are not linked they can allbe pointing in different directions at any given time. The assembly maytherefore be difficult to control.

With known load-carrying assemblies there is a tendency for thedirection of movement to be readily upset. A variety of means have beenemployed in an attempt to give improved steerability, but withoutsuccess. The present invention seeks to overcome the problems anddisadvantages of the prior art by providing a mechanism to retainsteerable wheels of a steerable assembly in a position allowing forstraight-forward motion, and which acts to return the steerable wheelsto the position which corresponds to straight motion for the assembly.Preferably this is regardless of the extent to which the steerablewheels may be caused to shift due to variations in terrain, etc.

In a further aspect, the present invention preferably acts to preventany tendency the assembly might exhibit to drift out of the positionwhich corresponds to straight ahead motion and compensate for thetendency of the assembly to steer in anything other than a straightline.

PRIOR ART

There has been very little development of steering systems forload-carrying assemblies of the present invention. For examplePCT/GB96/00687 discloses a trolley, such as a supermarket trolley,having a castor at each corner. The castors are arranged as a driving(rear) castor and as a driven (front) castor. A worm gear arrangementallows the driving castor on one side to drive the driven castor on thatside such that when the driving castor turns in one direction, thedriven castor turns in the opposite direction. However, there is nolinkage of the castors from one side to the other. Therefore, thecastors on one side could be turned to the right (rear) and left(front), and the castors on the other side could be turned to the left(rear) and right (front). This would defeat the entire exercise. Also itis only relevant for castors located immediately below the frame and isnot useable for any other form of wheel, nor for any other form ofproduct.

Furthermore, U.S. Pat. Nos. 4,348,033 and 4,405,140 relate to asteerable bob sled where the four runners of the sled are linked toenable them to be steered. However, the mechanism involved is a complexarrangement requiring numerous parts, with the use of cables and links.Furthermore, it is intended to controlled from within rather thanwithout. This is a fundamental difference in that when controlled fromwithin there is an occupant who can steer the apparatus and it is notintended to be steered by external forces. With a device such as aperambulator or child stroller, it is steered from without and istherefore intended inherently to be controlled by external forces.Furthermore, with devices such as perambulators and strollers, it isinherently intended that they not be controlled by internal forcesotherwise a wriggling child or baby could control the direction of theperambulator or stroller, and this is totally contrary to what isrequired.

BRIEF SUMMARY OF THE INVENTION

In accordance with a first aspect of the present invention there isprovided a moveable load-carrying assembly including a chassis having aplurality of wheels arranged as a first wheel set and a second wheelset, each wheel being rotatable and swivellable relative to the chassis;the wheels of the first wheel set being connected by a first linkage,and the wheels of the second wheel set being connected by a secondlinkage; and wherein one of the wheels of the second wheel set is linkedto the opposite one of the wheels of the first wheel set by a link suchthat when one of the wheels of the first wheel set is swivelled in onedirection relative to the chassis, all the wheels of the first wheel setswivel in that direction in unison and all the wheels of the secondwheel set swivel in the opposite direction in unison.

Preferably, there are two wheels in the front wheel set. Morepreferably, there are two wheels in the rear wheel set. Advantageously,the chassis has a front transverse member and a rear transverse member.More advantageously, the front transverse member is the front linkage.Furthermore, the rear transverse member may be the rear linkage.

Preferably, the link is a bar or rod pivotally attached to one of thefront wheels and to the diagonally opposite one of the rear wheels.

In accordance with a further aspect of the present invention there isprovided a moveable load-carrying assembly wherein means are included toprovide three distinct modes of operation for the rear set of wheels,the modes corresponding to straight-line travel (either forward or inreverse), folly-steerable travel (again either forward or in reverse),and a braking mode.

In accordance with another aspect of the present invention there isprovided an apparatus for controlling the direction of travel of asteerable assembly, the apparatus including:

(i) a first member associated with a tie-rod operably connected to oneor more steerable wheels of the assembly;

(ii) at least one further member associated with a fixed chassis memberof the assembly, the at least one further member being selectively andcontinuously pivotably moveable relative to the fixed chassis memberbetween respective inoperative and operative end positions; and

(iii) resilient means associated with the at least one further member,the arrangement being such that, in use, when the steerable wheels ofsaid assembly undergo a change in direction, the first member and the atleast one further member come into contact, whereby the resilient meansacts to return the at least one further member to its inoperativeposition, thereby correcting the steering of said assembly.

DESCRIPTION OF THE DRAWINGS

In order that the invention may be more clearly understood and put intopractical effect, there shall now be described preferred embodiments ofmoveable load-carrying assemblies in accordance with the presentinvention, the description being by way of non-limitative example onlyand being with reference to the accompanying drawings, in which:

FIG. 1 is a top plan view of a first embodiment of a chassis of amoveable load-carrying assembly;

FIG. 2 is a view similar to FIG. 1, showing the assembly of FIG. 1 inits configuration best suited for turning wherein all wheels aresteerable;

FIG. 3 is a cross-sectional view along the lines of and in the directionof arrows 3—3 of FIG. 1;

FIG. 4 is a view, similar to FIG. 3, of an alternative embodiment of anassembly in accordance with the present invention;

FIG. 5 is a partial top view of the alternative embodiment of FIG. 4;

FIG. 6 is top plan view of the embodiment of FIGS. 4 and 5, when in thestraight-ahead mode;

FIG. 7 is a view, similar to FIG. 6, but when turning left;

FIG. 8 is a side view of one of the rear wheels of the assembly of FIGS.4 to 7, when in its locked configuration, wherein all wheels are fixedagainst any swivelling, with the overall arrangement acting in aconventional manner;

FIG. 9 is a view similar to FIG. 8, showing a rear wheel of thealternative embodiment of FIG. 4 in a second configuration, wherein allwheels are swivellable;

FIG. 10 is a view similar to FIGS. 8 and 9 but showing the rear wheelsin a third configuration, being a braking mode;

FIG. 11 is a view taken along the lines of and in the direction ofarrows 11—11 of FIG. 10;

FIG. 12 is a side elevational view of an assembly in accordance with thepresent invention, with the alternative embodiment of FIGS. 4 to 11;

FIG. 13 is a partial view, in rear elevation, of a further embodiment ofthe present invention incorporating a centralising mechanism; and

FIG. 14 is a view, similar to FIG. 13, of an alternative form of acentralising device or mechanism in accordance with the presentinvention.

DESCRIPTION OF PREFERRED EMBODIMENTS

With reference now to FIGS. 1 to 3, there is illustrated a chassis madeup from an interconnected arrangement of respective front and reartransverse members 2 and 3 respectively, and co-operating longitudinalmembers 4. The members 2, 3 and 4 make-up the chassis 1 and areinter-connected in any known manner, as for example by welding, bolting,pinning, etc., to give a substantially rigid chassis 1. As shown in FIG.3, the members 4 are each an elongate member having a longitudinalportion 4 b and, extending from the rearward end thereof, an accurateportion 4 a, the accurate portions 4 a being adapted, in use, to receiveand preferably releasably retain a collapsible assembly which in turn isadapted to co-operate with a load-carrying means.

Mounted at or in the vicinity of each end of each of the transversemembers 2, 3 are wheel assemblies 5. Wheel assemblies 5 are made up of awheel 6, a stub axle 7 on which the wheel 6 is mounted for rotation, aswivel axle 8 fixedly connected to the transverse member 2, 3, and aboss 9 pivotably mounted relatively to the swivel axle 8, preferablywith the use of brushings or bearings of an appropriate type. The boss 9is rotatably yet releasably mounted relative to the swivel axle 8 by useof a split pin or the like. The stub axle 7 is associated with the boss9 in such a way that it is substantially at right angles to swivel axle8. Each wheel 6 is rotatable about its stub axle 7, and also pivotableor swivellable relative to the chassis 1, around the respective swivelaxle 8. In an alternative (not shown) a caster, made-up of twojuxtaposed wheels with each wheel mounted for rotation on a free end ofa stub axle, is mounted, via a boss and pintle, for pivoting orswivelling movement relative to the chassis 1.

One of the front wheels 6 is connected via a suitable linkage 11 to theopposed one of the rear wheels 6. The front wheels 6 are linkedtogether, in any suitable manner, and the rear wheels 6 are also linkedtogether. The end result of such an arrangement is that all four wheels6 are steerable, with the front and rear pairs of wheels beingrespectively moveable in opposite directions.

With reference now to FIGS. 1 and 2, each boss 9 has associatedtherewith, and extending at an angle therefrom, an attachment member 20.The attachment members 20 are preferably somewhat boomerang-shaped sothat the front portion 20 a thereof may, if desired, contact thelongitudinal member 4 prior to the wheel 6 making contact therewith,thus acting as a limit to the swivel action of the wheels 6 relative tochassis 1. The attachment members 20 associated with the rear wheels 6are interconnected via a rear linkage 21, and the attachment members 20associated with the front wheels 6 are interconnected via a frontlinkage 22. One of the rear wheels 6, and the opposed (diagonal) one ofthe front wheels 6, has associated therewith a further member 23 fixedlyattached to the boss 9 and extending at an angle to both the boss 9 andthe attachment member 20. The two further members 23 are interconnectedvia the link 11 so that when the rear wheels 6 are pivoted or swivelledin a given direction about their swivel axles 8, the front wheels 6pivot or swivel in the contrary direction about their respective swivelaxles 8. In such a way fully controllable steering for the overallchassis 1 and associated wheel assemblies 5 is achieved. The assembly issuch that each wheel 6 is subjected to or operates in a caster-typeaction.

A body to be attached to chassis 1 would preferably be attached to frontlinkage 22 at points a (FIG. 1), and preferably pivotally attached atthe rear at b (FIG. 3). In this way the body can be used to control thedirection of the front wheels 6 by acting directly on link 22 to thuscontrol the relevant wheels 6.

With reference now to FIGS. 4 to 12 of the drawings, there isillustrated an alternative embodiment of a moveable load-carryingassembly. The same numbering system is employed as with the embodimentof FIGS. 1 to 3. The alternative embodiment includes a chassis 1 made upfrom an interconnected arrangement of respective front and reartransverse members 2, 3 and co-operating longitudinal members 4. Thevarious members 2, 3 and 4 making up the chassis 1 are connectedtogether in any known manner, as for example by welding, bolting,pinning, etc., to give a substantially rigid structure.

There may be two front transverse members 2, mounted one above theother; and two rear transverse members 3, also mounted one above theother. The longitudinal members 4 extend between them. The actualconfiguration for the chassis 1 does not constitute an essential part ofthe invention.

Mounted at or in the vicinity of each end of each of the transversemembers 2 and 3 are wheel assemblies 5. The assemblies 5 are made up ofa single wheel 6, a stub axle 7 on which the wheel 6 is mounted forrotation, a swivel axle 8 fixedly connected to and extending between thepairs of transverse members 2 and 3, and a boss 9 pivotably mounted onthe swivel axle 8, preferably with bushings or bearings of anappropriate type. The bosses 9 are rotatably yet releasably mountedrelative to the swivel axle 8. The stub axle 7 is associated with theboss 9 so that it is substantially at right angles to the swivel axle 8.As a result, the wheel assemblies 5 have a caster action, beingswivellable relative to the chassis 1.

One of the front wheels 6 is connected via a suitable link 11 to theopposed one of the rear wheel 6. The front wheels 6 are linked togetherin any suitable manner; and the rear wheels 6 are also linked together.Preferably, the boss 9 for each front wheel assembly 5 is fixedly, yetpivotably, connected to a further linkage—in the form of a rod or thelike extending transversely of the chassis 1. In like manner the opposedrear wheel assemblies 5 are fixedly yet pivotably linked, by means of afurther transverse member or linkage. The end result of such anarrangement is that all four wheels are steerable.

In like manner to the embodiment of FIGS. 1 to 3, the boss 9 of the atleast one of each of the front and rear wheel assemblies 5 hasassociated therewith and extending at an angle therefrom a furthermember 23. The further members 23, of opposed ones of the front and rearwheels 6, are interconnected by the link 11. Attachment members 20 ofthe boss 9 of the front wheels 6 are interconnected via linkage 22 tohave the front wheels pivotable (swivellable) in unison relative to thechassis 1. In a similar manner, the opposed rear wheels 6 areinterconnected via a linkage 21, to have the rear wheels 6 alsopivotable (swivellable) in unison. The end result is that when the rearwheels 6 are pivoted or swivelled in a given direction relative to thechassis about their respective swivel axles 8, the front wheels 6 pivotor swivel in the opposite direction.

If desired, for this embodiment, the transverse members 2, 3 may becombined into a central transverse member this making chassis 1approximately H-shaped. Alternatively, transverse members 2,3 can bedeleted and replaced by a basket 29 of wire or the like which would besecurely and/or releasably mounted between longitudinal members 4, inwhich case the basket 29 adds to the structural strength of chassis 1,and would be considered part of chassis 1.

In the embodiment illustrated in FIGS. 4 to 10, the chassis 1 andassociated wheels 6 are able to be set in one of three operating modes,including:

(i) a first mode where all wheels 6 are lockable in direction yet arerotatable thereby facilitating straight-line motion either forward orreverse;

(ii) a second mode where the wheels 6 are steerable, being bothrotatable about their respective stub axles 7 and swivellable abouttheir respective swivel axles 8; and

(iii) a third mode where the rear wheels 6 are locked against rotation.

With particular reference to FIGS. 8 to 11, illustrated therein are thethree operating modes. Fixedly mounted to the at least one of the rearswivel axles 8 is a longitudinally and outwardly-projecting locatingmember 30. Associated with attachment member 20, now part of boss 9, foreach rear wheel 6, and pivotably mounted thereon and relative thereto,are respective lever members 31, each lever member 31 in turn beingconnected to an adjacent end of a linkage member 21 extendingtransversely of the chassis 1. The lever member 31 is pivotably attachedto attachment member 20 by any suitable means such as, for example, apin 33. The lever member 31 has extending therefrom and at substantiallyright angles thereto a stud 34 which co-operates with the shaped rearend portion of the attachment member 20 in a cam-follower typearrangement.

The lever member 31 is selectively movable between the three positionsillustrated in FIGS. 8, 9 and 10 respectively, each positioncorresponding to the three modes of operation. The application of aforce to the linkage member 21, as for example by the foot of anoperator, can impart movement to the assembly of linkage member 21 andassociated lever members 31, thereby moving the assembly to the desiredposition to achieve the desired mode of operation.

When in the position shown in FIG. 8, the lever member 31 engageslocating member 30, thereby preventing swivelling movement of the rearwheels 6—and in turn the linked front wheels 6—yet still allowing forrotation of the wheels themselves. In this mode, all wheels 6 are in aposition to allow straight ahead motion.

When moved to the position shown in FIG. 9, all wheels 6 are rotatable,and also swivellable, the overall assembly thus being steerable as isdescribed above.

When the lever member 31 is moved to the position shown in FIG. 10, thestud 34 contacts between internally directed projections 35 disposedaround the hub 36 of the rear wheels 6 to prevent rotation of the rearwheels 6.

With reference now to FIG. 12, there is illustrated a framework adaptedto receive, and releasably retain thereon, a suitable means forcontaining a load—as for example a tray or the like, a bassinette, etc.The arrangement as illustrated is adapted, in any known manner as forexample by pinning, to be releasably or fixedly connected to a steerablewheeled assembly of the type referred to earlier.

If desired, the locating member 30 may be incorporated into arcuateportion 4 a of longitudinal member 4 so that stud 34 can engage in asuitable slot or indentation (not shown) in arcuate portion 4 a.

When compared with known assemblies, the assembly of the presentinvention has been found to exhibit important advantages. As all wheelsare mechanically linked, and are capable of being used either in fixedwheel or fully steerable modes, all the advantages associated with afixed wheel assembly may be achieved, but without any of the inherentdisadvantages—as referred to earlier in the description—being associatedtherewith. Furthermore, the advantages associated with four-wheelsteerable assemblies are evident, again without the disadvantages. Thesame can be said with comparing the assembly of the present inventionwith known assemblies which employ four separate swivel wheel sets.

Also, as the wheels 6 are outside the periphery of chassis 1, there isno upper or lower limit on the diameter of wheels 6 so that largediameter wheels 6 may be used (to give a smoother ride) yet they arestill capable of being steered in the same manner, and to substantiallythe same extent, as smaller diameter wheels.

With reference to the embodiment of FIG. 13, it should be realised thatit is adapted to be disposed between a first, fixed bar or the likemember 201, constituting a lateral frame members of the chassis of aperambulator, pusher, trolley or the like equipment, and a moveable baror tie-road 202 extending laterally between steerable wheels of theperambulator, pusher, trolley or the like equipment.

The moveable tie-rod 202 will be moveable in the direction of the arrows(see FIG. 13) in response to swivelling of the wheels of the assembly,the swivelling of wheels could come about for a variety of reasons ordue to a number of factors.

A member 203 is affixed, in any known manner, as for example by welding,to the tie-rod 202 and adapted to extend substantially normallytherefrom. The member 203 may take the form of a rod-like member havinga rotatable means, as for example a roller 204, appropriately disposedat the free end thereof.

Extending normally from the fixed chassis member 201, in the directionof the tie-rod 202, are two spaced-apart substantially straight members205 and 206, each of which is pivotably moveable in the direction of thearrows relative to the fixed member 201. The pivotable movement can beachieved in any known manner, as for example by having the members 205and 206 pinned to the fixed member 201 at 207. Also extendingsubstantially normally from the fixed member, and interposed between thespaced-apart members 205 and 206, is a spacing means 208 intended tomaintain the spacing therebetween and being in the form of a protrusionattached to the fixed member 201 in any known manner, again as forexample by welding. The members 205 and 206 are interconnected at or inthe vicinity of the upper-most free ends thereof by a resilient member209 of any known type, as for example a spring.

The principle of operation of the centralising mechanism in accordancewith the embodiment of FIG. 13 is that as the tie-rod 202 is moved,either to the left or the right, in response to a change in thedirection of the wheels of the assembly, the roller means 204 engagesone of the members 205 or 206. As a result, member 205 or 206 will movein the direction of the arrow, downwardly towards the fixed chassismember 201, against spring pressure generated by the resilient means209. The resilient means 209 functions to attempt to return the member203 and associated roller means 204 to the position shown in FIG. 13,where it is disposed between the upper free ends of the opposed members205 and 206, but not in contact therewith. Therefore, the tie-rod 202 isforced to move in the opposite direction, thereby tending to straightenthe wheels of the assembly to the straight-ahead position. As can beseen, therefore, the mechanism acts to compensate for any tendency forthe assembly to steer in a direction other than straight, and also actsto return to the straight ahead position after it has been turned.

Each member 205, 206 has a substantially V-shaped cut-out 210 therein,which tends to apply uneven pressure to the roller means 204 as it movesout of the central position illustrated.

As only a single resilient means 209 is used to achieve the centralisingfunction, regardless of the direction of movement of the tie-rod 202,the arrangement acts in simplistic yet effective manner. There is, forexample, no need to select evenly balanced springs, which would havebeen the case if a single spring means was to be associated with eachmember 205, 206 since with the present arrangement the same force willbe applied to both steering directions.

With the embodiment of FIG. 13 as soon as the tie-rod 202 is shiftedaway from the position shown, which corresponds to straight-forwardmotion for the assembly, the spring 209 acts to attempt to return thetie-rod 202 to that position, thereby regaining straight-forward motion.The more off-set is the member 203 from the position illustrated due tovariations in terrain, or tightness of turning the greater is the springtension acting to return the member to the position illustrated.

The embodiment of FIG. 14 shows, in full lines, the arrangement intendedto steer the assembly in a straight line. In phantom there are shownwhat transpires when the assembly is affected in any way so as to betravelling in a direction other than straight ahead.

In similar manner to the embodiment of FIG. 13, the alternativecentralising mechanism of FIG. 14 is adapted to be disposed between afixed bar or the like member 301, constituting one of the lateral framemembers of the chassis of a perambulator, pusher, trolley or the likeequipment; and a moveable bar or tie-rod 302 extending laterally betweensteerable wheels of the perambulator, pusher, trolley or the likeequipment.

A member 303 is affixed in any known manner, as for example by welding,to the tie-rod 302 and is adapted to extend substantially normallytherefrom. The member 303 preferably takes the form of a rod-like memberhaving a rotatable means, in the form of a roller generally designated304, appropriately disposed in any known manner at the free end thereof.

Affixed to the fixed member 301 and adapted to be pivotably moveablerelative thereto are two arm members 305 and 306, the arm members 305and 306 being pivotably moveable relative to the fixed member 301 in thedirection of the arrows, dependent upon whether or not the assembly istravelling either to the left or right. The pivotable movement can beachieved in any known manner, as for example by having the arm memberspinned at 307 to the fixed member 301. A suitable resilient means, asfor example a spring 310, can be extended between the respective freeends of the arm members 305 and 306, the spring means 310 being providea bias to return the arm members 305, 306 to the position shown in fulllines in FIG. 14. Means are provided for limiting the extent ofpivotable movement of the arm members 305 and 306 relative to the fixedmember 301. Preferably, such means will take the form of pins 308 and309 on the fixed member 301 and intended to contact a surface of the armmember 305 or 306.

When in the position shown in full lines in FIG. 14, corresponding tothe straight ahead position, the roller 304 has no force applied theretoas the stop pins 308 and 309 act to prevent the arm members 305 and 306contacting roller 304.

As the tie-rod 302 moves either to the left or the right, the roller 304contacts open of the arm members 305 or 306 to force the relevant armmember in a downward direction, as illustrated by the arrows, againstthe pressure applied by the spring 310 until that edge of the arm memberresting against the roller 304 is substantially parallel to the fixedmember 301. When in that position no further pressure is applied to theroller 304. Therefore, the operator would feel resistance either side ofcentre until the relevant arm member 305 or 306 moves downwardly towardsthe fixed member 301 to its maximum possible extent, at which time thereis no further resistance to steering.

This will tend to hold the steering in the central position but wouldhave little if any effect on any other steerable position. The shape ofthe free end of the bar members 305 and 306 could be varied to vary the“feel” given to the steering assembly. In an embodiment not illustrated,the free end of the or each arm member 305, 306 could be curved in anupwards direction, giving rise to increased tension the further thesteering handle of the trolley was moved out of the straight-aheadposition. In the embodiment illustrated, however, the shape of the freeend of each arm member 305, 306 is such that spring tension is nullifiedwhen the overall assembly is steering in a direction other thanstraight-ahead.

The embodiment of FIG. 14 acts to counter any tendency for the steerablewheels of the assembly to “drift” away from the position correspondingto straight-ahead motion. In contrast to the embodiment of FIG. 13, theembodiment of FIG. 14 only acts within a predetermined range ofdisplacement of the tie-rod 302 and associated member 303.

It will be understood that the invention disclosed and defined hereinextends to all alternative combinations of two or more of the individualfeatures mentioned or evident from the text or drawings. All of thesedifferent combinations constitute various alternative aspects of theinvention.

It will also be understood that where the term “comprises” or itsgrammatical variants, is employed herein, it is equivalent to the term“includes” and is not to be taken as excluding the presence of otherelements or features.

The claims defining the invention are as follows:
 1. A moveableload-carrying assembly wherein means are included having a single leveroperable to provide three distinct modes of operation for a set ofwheels, the modes corresponding to straight-line travel (either forwardor in reverse), fully-steerable travel (again either forward or inreverse), and a braking mode.
 2. An assembly as claimed in claim 1, theassembly fitted to a hand-movable load-carrying assembly including achassis having a plurality of wheels arranged as a first wheel set and asecond wheel set, each wheel being rotable and swivellable relative tothe chassis; the wheels of the first wheel set being connected by afirst linkage, and the wheels of the second wheel set being connected bya second linkage; one of the wheels of the second wheel set being linkedto the opposite one of the wheels of the first wheel set by a link suchthat when one of the wheels of the first wheel set is swivelled in onedirection relative to the chassis, all the wheels of the first wheel setswivel in that direction in unison, and all the wheels of the secondwheel set swivel in the opposite direction in unison; and wherein eachwheel has a substantially vertical swivel axle about which it can swivelrelative to the chassis; a boss being mounted on each swivel axle, eachwheel being rotably mounted on a stub axle, each stub axle being mountedto its respective boss remote from the swivel axle to enable each wheelto act in the manner of a caster.
 3. An assembly as claimed in claim 2,wherein to each boss there is attached an attachment member, the firstlinkage connecting the attachment members of the first wheel set at theends thereof remote from the swivel axles.
 4. An assembly as claimed inclaim 3, wherein the attachment member extends outwards from boss ofeach wheel of the second wheel set, to each attachment member of thesecond wheel set there being pivotally attached a lever member, thesecond linkage being attached to the lever members at the ends thereofremote from the attachment members.
 5. An assembly as claimed in claim4, wherein the lever members are pivotable about the attachment memberto provide the three modes of operation.
 6. The assembly as claimed inclaim 4, wherein the second linkage member is operable by foot pressureto move the lever members to and from the three modes of operation. 7.An assembly as claimed in claim 5, wherein to the swivel axle of atleast one of the wheels of the second wheel set is fixedly mounted alongitudinally and outwardly projecting locating member; at least one ofthe lever members engaging with the locating member to provide thestraight-line travel mode.
 8. An assembly as claimed in claim 7, whereinthe locating member has a slot in the end thereof remote from the swivelaxle, the slot being adapted to receive therein a part of the levermember when in the straight-line travel mode.
 9. An assembly as claimedin claim 5, wherein at least one of the wheels of the second wheel sethas a hub on its stub axle secured to the wheel, the hub having aplurality of radially directed projections; the at least one of thelever members having a stud adapted to engage between the projections onthe hub to prevent rotation of the wheel and thus provide the brakingmode.
 10. The assembly as claimed in claim 9, wherein the attachmentmember has an opening therein to allow the stud to engage between theprojections, the opening having a surface which the stud contacts duringa part of the pivoting movement of the lever member between thestraight-line mode and braking mode of operation to provide thefully-steerable travel mode of operation.